Find substitute for mosfet in servo board of versacamm sp-540v plotter

[edugimeno]

Hi There!
I am currently serviciing a plotter versacamm sp-540v
I found a shorted mosfet labeled J553 which corresponds with SJ-553s (surface mount)
Neither local stores nor other webpages that are able to provide it before 1 month (only aliexpress, with 1 month delivery) can provide this part
I need to find a substitute for it. Can anyone give me a hint on a part that I can use to replace it?

Also, given the schematic Im attaching (pg 36, transsitor Q1) , does it make sense that the whole machine won't turn on when I press the POWER button on the panel? This part serves as a switch to start the heater so this kind of explains the spark I get as soon as I plug the PS DC wire to the board (indicating high current flowing even when powered off) but not sure if this makes sense with not being able to start the whole machine.

Thanks everyone in advance!

[R_J]

Re: Find substitute for mosfet in servo board of plotter

Check the fuses on the main board (page 30) one may be open. looks like they (vhv0,vhv1) supply +41v for the head drivers, If the fuses are ok it might be just the mosfet that shorted.

[edugimeno]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

Not sure if I checked them all but visually (on the board) I checked all the fuses I could see and they all were OK. Thanks

[edugimeno]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

Anyway can I just use ANY P-Channel mosfet with

• Vds>60v
• Vgs>20v
• Id>30A
• Gate Drive=4v

Being just a basic switching control gate to turn heating ON or OFF, which probably happens just once at the beginning and at the end of the printing process, I don't expect to have to meet other specs related to high frequency, max speed, etc, right?

Thanks!

[R_J]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

Almost any mosfet with those specs should be ok, it is just used as a switch, any 60v or higher, 30 amp or higher should be ok. If it was in a smps or a similar circuit, frequency etc could be an issue, but that's not the case here.

[edugimeno]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

Almost any mosfet with those specs should be ok, it is just used as a switch, any 60v or higher, 30 amp or higher should be ok. If it was in a smps or a similar circuit, frequency etc could be an issue, but that's not the case here.

Awesome, some parts selectors like RS allows to filter with all those parameters so I got some candidates, thank you!

[edugimeno]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

MM sill having issue identifying some specs. Do I need to care for Vgs(th)?
These MOSFET seems to trigger at 2-4v, is this normal? Do I need to select MAX Vgs=4?
If I don't select that I get many more results

[eccerr0r]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

You will rarely if ever find a mosfet with Vgs > 20V, in fact most mosfets 20V is the absolute maximum before you start destroying them (usually 30V or so is when you really start blowing them though).

Vgs characterization depends on the circuit driving it, and for replacement it must pretty much match the original else you may run into operational problems.

[edugimeno]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

Ok but about Vgs(th) the original mosfet states:

"4v gate drive device"

Does this mean it will need at least 4v to trigger? Or is this the maximum? Or is this just a frequent value so I can discard it?

I have attached the full triggering circuit, it comes from a 41v PS thru what to my limited knowledge seems like a 1/3.2 voltage divider which would deliver 12v??

I would appreciate some help here

Thanks

[eccerr0r]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

Now that I see the schematic, I think you best choose an identical device that closely matches the original due to the preheat circuit. This is a very poor design as the circuit depends on the characteristics of the device to operate the same as before. If you don't care about the preheat/slow power on then you can go ahead and use any p-ch mosfet there that meets the drain current requirements. TBH the preheat is probably what killed the device in the first place...

[edugimeno]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

Well I don't know if the preheat os slow heat function is used....But I don know that an identical-closely alike Q for this one is being impossible to find.
If ANY P-Channel that goes beyond 30A will work and I don't need to care for that "4v gate" spec, I will go ahead as Im totally stuck on this repair...
Thanks!!

[edugimeno]

Re: Find substitute for mosfet in servo board of versacamm sp-540v plotter

Ok this board is giving me more issues, I put it back today into the machine, without Q1 at all, expecting that despite the heating wouldn't work, at least the machine would some osme signs of "life", but it didn't go lthat way...
I will open a new thread as this is now a different matter, if those who provided help here want to take a look at it.

Link to new thread: https://www.badcaps.net/forum/showthread.php?p=1176211
Thanks!